The multilayer flexible wired circuit board, which is a flexible wired circuit board having a plurality of conductor layers, is being widely used in electronic equipment and parts in recent years, to meet the demand for electronic equipment and parts to have increasingly higher density. The multilayer flexible wired circuit board is usually produced in the method shown in FIG. 4.
Specifically, a double-sided substrate 4, in which a first conductor layer 2 and a second conductor layer 3 are laminated on both sides of a first insulating layer 1, respectively, is prepared, first, as shown in FIG. 4(a). Then, a second insulating layer 7 and a third insulating layer 8 are laminated on the first conductor layer 2 and the second conductor layer 3 of the double-sided substrate 4 through a first adhesive layer 5 and a second adhesive layer 6, respectively, as shown in FIG. 4(b).
Also, a first single-sided substrate 11 in which a third conductor layer 10 is laminated on a fourth insulating layer 9 and a second single-sided substrate 14 in which a fourth conductor layer 13 is laminated on a fifth insulating layer 12 are prepared separately, as shown in FIG. 4(c). Then, a first cover insulating layer 16 is laminated on the third conductor layer 10 of the first single-sided substrate 11 through a third adhesive layer 15, and a second cover insulating layer 18 is laminated on the fourth conductor layer 13 of the second single-sided substrate 14 through a fourth adhesive layer 17, as shown in FIG. 4(d).
Then, the fourth insulating layer 9 of the first single-sided substrate 11 is laminated on the second insulating layer 7 laminated on the double-sided substrate 4 through a fifth adhesive layer 19, and the fifth insulating layer 12 of the second single-sided substrate 14 is laminated on the third insulating layer 8 laminated on the double-sided substrate 4 through a sixth adhesive layer 20, as shown in FIG. 4(e).
This method has the problem that the multiple flexible wired circuit board thus produced provides increase in number of layers and thus increase in thickness so that it cannot meet the demand in recent years for thinner lamination of wired circuit board.